Recent reports indicate that several possible mechanisms may exist for the maintenance of specific acquired immunological tolerance. These mechanisms may be dependent on the antigen (polymorphic vs. homogenous) used, certain non-specific host factors etc. It is the purpose of this proposed project to: 1) study the effect of the age of the host on the mechanism of the maintenance of specific tolerance; 2) study the effect of the nature of the tolerogen (polymorphic vs. homogenous) on the maintenance and termination of specific tolerance; 3) determine the number and location of carrier and antigenic determinants on an antigen molecule. All of these are designed to promote further understanding of the basis of immunological tolerance, the events occuring during termination, and the possible mechanism of autoimmunity.